In the molding devices currently in use today, the two mold halves open substantially symmetrically on each side of the parting plane, this being a solution which, from a technological standpoint, is easy to implement. For their part, insertion or loading means designed to introduce a parison into the mold and extraction means designed to extract a molded container from the mold are arranged in such a way that the movement of the gripper, in both cases, is approximately in the parting plane of the mold in the mold or in close proximity thereto.
What is more, it is commonplace for the molding device to be arranged in the form of a rotary device of the carousel type, generally equipped with a number of molds distributed about its periphery, the parting planes of these molds being substantially radial. For their part, the insertion means and the extraction means are designed in the form of rotary transfer wheels equipped with grippers supported by approximately radial arms. The time needed by the insertion means to introduce the parison radially into the mold or by the extraction means to extract the container radially from the mold means that each gripper follows the mold over a portion of the rotary path thereof, and, in addition, the gripper also has a movement with a radial component so as to enter or leave the mold, these movements having to be performed without any physical interference between the edges of the mold halves and the grippers and either the parison or the container respectively.
This results in a relatively complicated arrangement of the insertion and extraction means which are in the form of transfer wheels equipped with gripper support arms driven in a double pivoting and radial movement while the grippers may, for their part, be driven in a pivoting movement at the end of their support arms. These combined movements are obtained mechanically through complex collections of rollers collaborating with fixed cams, and mean that the surroundings of the rotary carousel are very cluttered. In addition, these assemblies cause significant mechanical friction as well as some degree of rebound, and this limits the rate at which the installations can operate.
Recently, simplified structures have been proposed, these resorting to an arrangement of one-piece gripper and support arm assemblies driven in a single pivoting movement, thus considerably simplifying the controls and removing an appreciable amount of clutter from the immediate confines of the rotary carousel while at the same time allowing appreciably increased operating rates. However, this simplification has only been able to be achieved at the expense of a misalignment which, while admittedly small, is nonetheless real enough, between the axis of the parison or of the container and the parting plane of the mold at the beginning of insertion or, respectively, at the end of extraction. In other words, the movements of the gripper during insertion of the parison and during extraction of the container are now performed in arcs of a circle, rather than strictly radially. This may, at least in certain operating configurations, lead to the risk of physical interference between the edge of one of the mold halves and the gripper and/or the parison or container respectively.
Admittedly, one solution might have been to increase the angle of opening of the molds with respect to the angle of opening actually used. However, there are at least two reasons why such a solution would not prove satisfactory.
One first reason is that opening a mold through a larger angle leads to an increase in the time needed for the steps of opening and closing the mold, and this goes against the current demands of users who are wanting increasingly short times in order to increase production rates.
Another reason is that an increased angle of opening of the molds involves more available space and therefore entails spacing the molds further apart at the periphery of the carousel. That can be achieved only by increasing the diameter, and therefore the inertia, of the carousel which is something which, once again, would go against the current demands of users who are requiring increasingly compact machines and increasingly high production rates. Furthermore, a carousel of a larger diameter would be more expensive.